Intramedullary rod instrument

ABSTRACT

A femoral instrument for use in the intramedullary canal is described and includes an intramedullary rod having a tip at a free end. A body is attached to the intramedullary rod and has a face with a bone abutting portion. A centralizer mechanism is located within the rod and is operable to deploy and retract a plurality of members to engage and disengage an inner surface of the intramedullary canal. The length of the intramedullary rod from the tip to the face of the body is less than 30 cm. The instrument can also include an angular adjustment mechanism. The angular adjustment mechanism can have a plurality of formations and can be rotated about the longitudinal axis of the intramedullary rod to present at least a one of the formations to abut a portion of the body to define the relative angle between the body and the intramedullary rod.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.12/678755, filed Jul. 22, 2010 (now U.S. Pat. No. 8,636,741), which is aNational Stage 35 U.S.C. 371 of International Patent ApplicationPCT/GB2008/003183, filed Sep. 19, 2008.

BACKGROUND OF THE INVENTION

The present invention relates to a surgical instrument, and inparticular to a surgical instrument including an intramedullary rod.

Intramedullary rods can be used in knee arthroplasty procedures toprovide a reference to which a cutting guide or block can be attachedfor performing a femoral cut. It will be appreciated that the presentinvention relates to intramedullary rods which provide a reference orsome other feature or component which is used during preparation of thebone rather than to the type of rods which are placed inside theintramedullary canal to and secured with bone screws or similar as usedto repair broken bones or in other trauma type applications.

Intramedullary rods typically are of order 40 cm or so long from the tipof the rod to the bone engaging formation which engages the bone surfacein use. The end of the rods of such length become fixed in theintramedullary canal and so are self locating. However, theintramedullary canal varies from patient to patient in terms of itswidth, direction and straightness and so the intramedullary rod positioncan be compromised when using such long rods. Hence, the positioning ofcomponents attached to the rod, such as a cutting block, can also becompromised, and it can be difficult if at all possible to correctlyposition the cutting block.

It can be desirable to provide some angular adjustment so that theangular orientation of the cutting guide or block can be changed eitherto compensate for patient anatomy or otherwise to allow the femoral cutto be made at a preferred angle.

Intramedullary rods which allow angular adjustment exist, but they canbe difficult to use in practice. FIG. 1 shows an existing assembly 10including an intramedullary rod 12 which is pivotably attached to a bodyby a pivot mechanism 14 which can be operated by a user to selectivelychange the angle of the rod, for example, by operating a lever 16 toengage/disengage teeth to allow the rod to freely pivot. Hence the angleof the rod 12 can be adjusted relative to a cutting block 18. However,such prior pivoting mechanisms can be difficult to use in practice. Thelever to be operated is often small and difficult to operate with therod 12 inserted into the femur 20. Also, because of the construction ofthe pivot mechanism, very little space can be available for thedifferent selectable angles and so it can be hard to ensure that thecorrect angle is selected. Furthermore, there can be very little spaceavailable on which to display any scale so that the user can either seeor check the angle that they want.

Therefore, it would be desirable to provide an intramedullary rod withangular adjustment which can be used more easily and/or which can belocated in the intramedullary canal more easily.

The present invention provides a femoral instrument including a shortintramedullary rod with a centraliser mechanism so that the short rodcan be self centralised in the intramedullary canal allowing the rod andother components attached to the rod to be more easily positionedrelative to the bone in use.

The present invention also provides a femoral instrument including anintramedullary rod with an angular adjustment mechanism adapted to makethe instrument easier to use in terms of its operation and reading ofits scale.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda femoral instrument, comprising: an intramedullary rod; a body to whichthe intramedullary rod is pivotably attached; and an angular adjustmentmechanism, wherein the angular adjustment mechanism has a plurality offormations and is rotatable to present at least a one of the formationsto abut a portion of the body to define the angle between the body andthe intramedullary rod.

Preferably, the angular adjustment mechanism is rotatable about alongitudinal axis of the intramedullary rod.

The plurality of formations can be of various type and number. Theplurality of formations can be recessed or can stand proud of asupporting surface. The formations can be individual elements or pluralelements can make up a single formation. The formations can provide asurface or at least a part of a surface for abutable against a portionof the body. A formation or a plurality of formations can be provided onthe body to interact with or co-operate with the formations of the angleadjustment mechanism.

The plurality of formations and the portion of the body can providebetween them at least a first or a plurality of male members and/or atleast a first or a plurality of female members and the male and femalemembers can be adapted to engage, mate or otherwise co-operate with eachother to define a plurality of different angles. Preferably, theplurality of formations and the portion of the body provide between thema rib and/or a plurality of slots in which the rib can engage. Each ofthe plurality of slots can be provided by a pair of recesses or notches.Preferably, the rib is provided on the body and the plurality of slotsare provided on the angular adjustment mechanism.

The plurality of formations can provide at least two different anglesand preferably at least three different angles, e.g., 3, 5 and 7degrees, although a greater number of different angles can also beprovided. The plurality of formations can provide a change in angle toboth the left side and the right side of the instrument.

The angular adjustment mechanism can bare a plurality of indiciaindicating the angular adjustment of the intramedullary rod. The indiciacan be arranged on the adjustment mechanism so that an indiciaindicating the angular adjustment corresponding to a current rotationalposition of the adjustment mechanism is presented to a user in normaluse of the instrument, for example on an upper most surface of theangular adjustment mechanism.

The angular adjustment mechanism can be translatable along thelongitudinal axis of the intramedullary rod to allow a different one ofthe plurality of formations to be selected.

The instrument can further include a biassing device which urges theangular adjustment mechanism toward the body to cause the at least oneof the formations to abut the portion of the body.

The instrument can further include a handle. The angular adjustmentmechanism can be translatable relative to the handle.

The instrument can further include a lock to lock the position of theangular adjustment mechanism.

The angular adjustment mechanism can include an element having agenerally polygonal transverse cross section and being centrally mountedto be rotatable about the longitudinal axis of the rod. The element canhave a plurality of generally flat faces. Each flat face can bare anindicia indicating an amount and/or a direction of angular adjustment.Preferably, the element, has a hexagonal, octagonal or decagonal crosssection.

The instrument can further including a plurality of members deployablefrom within the Intramedullary rod to outside the intramedullary rod.The plurality of members can be effective to centralise the position ofthe Intramedullary rod within an intramedullary femoral canal whendeployed. Preferably at least three members are provided. The memberscan be in the form of fins.

The instrument can further include a handle. The handle can include abutton operable by a user to deploy the plurality of members. The buttoncan be operable to drive a shaft or member extending at least partiallyalong the interior of the intramedullary rod and linked to the members.

The length of the intramedullary rod from a bone engaging face of thebody to a tip of the intramedullary rod can be less than 30 cm. Thelength of the intramedullary rod can be not more than 25 cm and morepreferably not more than 20 cm. The length of the intramedullary rod canbe between approximately 10 cm and 25 cm, more preferably betweenapproximately 15 cm and 20 cm, and most preferably between approximately15 cm and 18 cm. It has been found that making the rod too shortprevents it from centralising in the intramedullary canal as the innerdiameter of the canal is too great and that making the rod too longprevents the rod from becoming self-centralising as the plurality ofmembers cannot act to locate the rod in the centre of the canal asmovement of the tip or distal end of the rod is too constrained by thelocal geometry of the intramedullary canal.

A further aspect of the invention provides a femoral instrument,comprising an intramedullary rod having a tip at a free end; a body towhich the intramedullary rod is attached and having a face with a boneabutting portion; and a centraliser mechanism located within the rod,wherein the centraliser mechanism is operable to deploy and retract aplurality of members to engage and disengage an inner surface of anintramedullary canal, and wherein the length of the intramedullary rodfrom the tip to the face of the body is less than 30 cm, and preferablyless than 20 cm.

The further aspect of the invention can include one or more of thepreferred features of the first aspect of the invention mentioned above.

A yet further aspect of the invention provides a method of stabilising asurgical device relative to a bone using an instrument having anintramedullary rod extending from a body having a bone engaging surfaceand further comprising a centraliser mechanism, comprising: introducingthe intramedullary rod into the intramedullary canal of a patient withthe centraliser mechanism in a non-deployed state; and operating theinstrument to deploy the centraliser mechanism so as to stabilise theposition of the tip of the intramedullary rod within the intramedullarycanal.

The length between a tip of the intramedullary rod and the bone engagingsurface can be less than 30 cm, less than 20 cm or between approximately15 cm and 18 cm.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, and with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of a prior art femoral rod with angularadjustment;

FIG. 2 shows a perspective view of a femoral instrument according to theinvention;

FIG. 3 shows a side view of the femoral instrument of FIG. 2;

FIG. 4 shows a sectional view of the femoral instrument along line AA ofFIG. 3;

FIG. 5 shows a handle end view of the femoral instrument of FIG. 2;

FIG. 6 shows a tip end view of the femoral instrument of FIG. 2;

FIG. 7 shows a longitudinal cross sectional view through the tip of theinstrument illustrating a part of a centraliser mechanism of theinvention;

FIG. 8 shows a perspective view of a flares part of the centralisermechanism shown in FIG. 7;

FIG. 9 shows a partial sectional view of the flares part shown in FIG.8;

FIG. 10 shows a perspective view of the centraliser mechanism in aretracted state; and

FIG. 11 shows a perspective view of the centraliser mechanism in adeployed state.

Similar items in different Figures share common reference numeralsunless indicated otherwise.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a perspective view of an instrument 30 according to thepresent invention. FIG. 3 shows a side elevation of the instrument 30,FIG. 4 a cross-section through the instrument along line AA of FIG. 3,FIG. 5 an end view of the instrument from a handle end and FIG. 6 an endview of the instrument from a tip end. FIG. 7 shows a magnified crosssectional along line AA including the tip of the instrument illustratinga centraliser mechanism and FIGS. 8 and 9 are perspective views of partsof the centraliser mechanism. FIGS. 10 and 11 are perspective viewsillustrating the centraliser mechanism in use.

The instrument 30 includes an intramedullary (IM) rod 32, a body 34, anangular adjustment mechanism 36 and a handle 38.

The rod 32 has a generally tubular construction and includes a tip 40 ata free end thereof. Three apertures 42 are provided toward the free endof the rod. Within the rod three fin members 102, 104, 106 are providedwhich can be deployed from within the rod to exterior to the rod throughrespective apertures 42. The fin members can be deployed by operating abutton 44 located in handle 38 to actuate a shaft or drive member 46 toslide within rod 32 to deploy the fins. The fins are attached by alinkage to shaft 46 so that when the shaft moves along the rod, thelinkage causes the fins to be driven outwardly. The instrument alsoincludes a fin retraction button 45 in an upper portion of the handle 38operable by a user to retract the fins back within the rod. The finretraction button 45 is connected to the shaft and when the retractionbutton 45 is actuated by a user, the shaft 46 moves back along thelongitudinal axis of the rod, the linkage operates to draw the fins backwithin the rod and the rod returns the fin deployment button 44 backinto an initial position from which the button 44 can be operated againto deploy the fins. Hence, the deploying and retracting the centralisingand stabilising mechanism of the instrument is provided by an entirelymechanical mechanism. A spring (not shown) is provided as part of theinstrument to urge the rod away from the tip 40 so that the fins 102,104, 106 are normally in a non-deployed state. When button 44 isoperated, the rod is driven against the biassing effect of the springand a ratchet mechanism (not shown) interacts with the rod to hold therod at a position along the longitudinal axis of the instrument. Button45 interacts with the ratchet mechanism so that when button 45 isoperated, the ratchet is released and the spring acts on the rod todrive the rod back toward the handle thereby withdrawing the fins. Theoperation of the fins members will be described in greater detail belowwith reference to FIGS. 7 to 11.

The body 34 has a generally plate-like construction and presents a flatfemoral contact surface 48 toward the rod end of the instrument. The rod32 is pivotably attached to the body 34 so as to allow relative pivotingbetween the body 34 and rod 32, as will be described in greater detailbelow. As illustrated particularly in FIG. 4, the pivot includes a pin50 passing through a slot 52 in the drive member 46 so as to allow thedrive member 46 to translate along the longitudinal axis of the rodwhile also allowing the rod 32 to pivot relative to body 34.

A rear face 56 of body 34 bears a rib 58 projecting away from body 34and standing proud thereof. Rib 58 extends laterally across body 34 ofthe instrument. Rib 58 provides a part of the angular adjustmentmechanism for the instrument as will be described in greater detailbelow.

Body 34 also includes first and second cylindrical formations 60, 62accepting first and second pegs 64, 66 onto which a cutting guide andadjustment assembly 70 can be releasably attached.

Handle 38 is a generally hollow cylinder with upper and lower concaveportions providing a grip for a user. The rod 32 terminates within thebody of the handle which also includes button 44 and shaft 46 asdescribed above. Handle 38 is attached to rod 32 to prevent relativerotation about the longitudinal axis of the rod. Between handle 38 andbody 34, the angular adjustment mechanism 36 is provided.

The angular adjustment mechanism 36 further includes a first collar 72and a second collar 74. The first collar 72 is mounted on an extensionof the handle 38. The second collar 74 is mounted on an extension of thefirst collar 72 and extends around, and is centred on, the rod 32. Thefirst and second collars are slidably mounted so as to the translatablealong the longitudinal axis of the rod 32. A biasing spring 72A isprovided in the second collar 72 to urge the first and second collarstoward the body 34 in normal use. The first collar 72 is rotatable aboutthe longitudinal axis of rod 32 in order to lock the second collar 74 inposition.

The second collar 74 has a generally hexagonal cross-sectional shape. Anend of collar 74 adjacent body 34 includes six notches, three pairs ofwhich define three slots into which rib 58 can be accepted. Each notchof a pair of notches has a different depth, as particularly illustratedin FIGS. 3 and 4. Hence, when a pair of notches abuts against rib 58,the body 34 pivots relative to the longitudinal axis of rod 32 therebychanging the angular orientation between body 34 and rod 32.

The difference in depth between a pair of notches can be selected toprovide the third changes in the angular orientation of the rod relativeto the body away from the perpendicular. For example, in the illustratedembodiment, the depths of the notches are selected to provide 3, 5 or 7degrees of angular variation. With a pair of notches in a firstorientation, the relative angle can be changed in the right-hand orleft-hand direction. By rotating the collar 74, it will be appreciatedthat the same pair of notches is provided, but rotated through 180degrees, thereby providing the same magnitude of angular adjustment butin the opposite direction.

Flat outer surfaces of the collar 74 bear indicia 78 indicating thedegree and direction of angular adjustment. The indicia are arranged onthe collar 74 so that the degree and direction of angular adjustmentwith the collar in a current position is displayed on an uppermostsurface of the instrument for ease of reading by the user. For example,as illustrated in FIG. 2, with the collar in the current position, athree degree to the left angular adjustment will be provided. It will beappreciated that in other embodiments, different magnitudes of angularadjustment can be provided and a grace number, or fewer number, of pairsof notches can be provided.

It will also be appreciated that combinations of formations other thanthe rib and slot arrangement described can be provided. For example, inother embodiments, a rib may be provided on collar 74 and slots providedon body 34. Also, it is not necessarily essential to use a rib and slotsand any other combination of formations which allows non-parallelsurfaces of the collar 74 and body 34 to abut to cause pivoting of thebody, can be used. However, the slot and rib mechanism described hereinhas been found to be particularly usable in a surgical environment.Further, the collar 74 provides a large surface area on which theindicia can be displayed thereby facilitating ease of use of theinstrument as the indicia are sufficiently large to be easily readableand are also locating in a position where they can be easily read by theuser of the instrument while using the instrument.

A cutting guide assembly 70 is mounted on body 34. The cutting guideassembly 70 includes a cutting guide 80 having a slot therein forreceiving a saw blade and a plurality of holes or other apertures forreceiving drills and other cutting instruments as required, depending onthe particular procedure being carried out. The cutting guide 80 ismounted on an adjustment component 82 including a threaded mechanismallowing the cutting guide 80 to be translated back and fourth in adirection generally perpendicular to the bone engaging phase 48 of body34. A wheel 84 and lock 86 are also provided to allow the translationalposition of the cutting guide 80 to be adjusted and to lock the cuttingguide in place.

As best illustrated in FIGS. 7 to 11, the centraliser mechanism includesthree members or fins 102, 104, 106 arranged at approximately 120 Eintervals about the longitudinal axis of the instrument. The members areattached by a linkage mechanism to rod 46 which can be manually operatedby button 44 to cause the members to be deployed. The three members aremade from a single piece of flexible, preferably plastics, material 108which has three portions of reduced thickness 110, 112, 114 whichprovides a mechanical hinge by which the individual members can bendaway from their common core or body 108 by which they are attached tothe rod 46.

Each member has an outer, bone engaging part 116, 118, 120 which is madeof a harder or less flexible material than the core or body part of themembers. This composite construction of the members allows the membersto be flexed while still presenting a sufficiently robust bone engagingsurface to allow the members to centralise the rod when they engage theinner surface of the intramedullary canal. As illustrated in FIG. 9, bythe partial cross section through member 102, the outer part of themember 116 can include a projecting part in the form of a rib which canbe push fit received in a corresponding mating slot 120 in the lowerbody part of the member 102. Suitable materials for the body part of themembers are, for example, thermoplastics, ABS or PPSU. Suitablematerials for the outer parts include, for example, polypropylene orpolycarbonate.

The tip 40 has an inner end which has a sloped face 124, or faces whichare presented to sloped, curved or chamfered free ends of the members,e.g. 126, so that the free ends of the members 102, 104, 106 will camover the sloped face 124 of the tip and ride over the tip to deploy themembers, when driven by the rod, as best illustrated in FIGS. 10 and 11.The outer casing of the instrument 32 can include three grooves in itsouter surface extending along the longitudinal axis and positioned toreceive and guide the bottom parts of the members as they are deployed.As described above, a ratchet mechanism holds the rod in position sothat the members are retained in their deployed state illustrated inFIG. 11, until the ratchet is released by the user operating button 45,at which time the spring acting on the rod drives the rod back towardthe handle part and the members return to their non-deployed statewithin the rod 32 as illustrated in FIGS. 10 (in which the rod is notshown) and 7.

The parts of the instrument can be made of suitable plastics materialsand metals. Many of the components of the instrument can be made frombiocompatible plastics, such as polypropylene, ABS, polyethylene andpolyurethane and the rod 32, and any other preferably metal components,can be made from a suitable biocompatible metal, such as stainlesssteel.

Having described the instrument, use of the instrument in a kneearthroplasty procedure will now briefly be described.

Conventional IM rods are typically approximately 30 to 40 cm long andare introduced into the IM femoral canal to the level of the isthmuswhere the canal profile is at its narrowest and secures the IM rod inthe proximal position. Various other components can then be assembled onthe IM rod including a cutting block for performing the distal cut. Suchrods are fluted to relieve IM pressure and permit the release of bonemarrow in order to avoid embolisation. However, in some cases, the rodmay not be able to extract enough bone marrow and part of it can stillbe pressed in the canal. This can cause migration of the bone marrowinto blood vessel and consequent occlusion which leads to embolism.Hence, there are deficiencies in using long IM rods.

The instrument of the present invention has a relatively short IM rod.That is, the length of the IM rod between the bone engaging surface 48and tip 40 is approximately 15 to 20 cm long. Hence, the tip 40 of therod will not automatically be located in the narrowest part of thefemoral canal and secured there. Instead, the fins can be deployed toprovide a centraliser mechanism to centre the rod in the IM canal afterit has been inserted, in order to avoid damaging the canal itself whilethe rod is introduced.

Hence, in use, the IM rod portion 32 is introduced into the IM canal ofthe femur until surface 48 of the body abuts against the condyles of thefemur. When in position, the surgeon can operate button 44 to deploy thefins so as to centralise the rod within the IM canal and also stabilisethe rod in position.

The cutting guide 80 is attached to body 34 and therefore the cuttingguide 80 has the same angular orientation with respect to rod 32 as body34. In order to adjust the angular orientation, the surgeon pulls thecollar 74 toward handle 38 and then rotates the collar 74 until thedesired angular adjustment is displayed on the uppermost surface. Thecollar is then released by the surgeon and the biasing spring 72A urgesthe collar 74 to engage the selected pair of notches with the rib 58 sothat the body 34 pivots relative to the longitudinal axis of the rod 32.

If the surgeon wants to select a different size of angle or direction ofangle, then the collar is again pulled towards the handle, rotated intothe correct position and released to engage the rib again. When theappropriate angle and direction has been selected, then second collar 72can be rotated to lock the adjustment mechanism in place. The cuttingguard assembly 70 can then be adjusted to translate the cutting guide 80to the desired height and the cutting guide 80 can then be pinned inplace on the femur. The cutting guide 80 can then be released from theinstrument by turning knob 86 to separate the instrument from thecutting guide 80 in one step and the instrument removed leaving thecutting block pinned in place. The remainder of the surgical procedurecan be continued as usual.

It will be appreciated that the angular adjustment mechanism of theabove described instrument is easy to use within a surgical environmentas a large element is provided for adjusting and selecting the desiredangular orientation. Further, any large surface areas provided on whichthe selected angle and direction can clearly be displayed and easilyread during normal use of the instrument. Therefore, the presentinstrument provides the flexibility of angular adjustment of the IM rodwithout introducing any increased difficulty in reliable use of theinstrument.

The invention claimed is:
 1. A femoral instrument, comprising: anintramedullary rod having a longitudinal axis; a body to which theintramedullary rod is pivotably attached, the body having a proximalportion; a first collar and a second collar disposed about theintramedullary rod, the second collar disposed between the first collarand the body, the second collar having a proximal and a distal end and aplurality of formations formed on the distal end of the second collar,the second collar being rotatable about the longitudinal axis to presentat least one of the plurality of formations to abut the proximal portionof the body and thereby define a relative angle between the body and theintramedullary rod, wherein the second collar is translatable along thelongitudinal axis; and a spring disposed between the body and the firstcollar to urge at least the second collar toward the body.
 2. Theinstrument of claim 1, wherein the plurality of formations and theproximal portion of the body provide between them a rib and a pluralityof slots, the plurality of slots being sized to accept the rib.
 3. Theinstrument of claim 2, wherein the body comprises the rib and the distalend of the second collar has the plurality of slots.
 4. The instrumentof claim 1, wherein the second collar has an outer surface that has aplurality of indicia indicating the angular adjustment of theintramedullary rod.
 5. The instrument of claim 1, further comprising ahandle mounted to the first collar.
 6. The instrument of claim 1,wherein the spring is disposed at least partially within the secondcollar.
 7. The instrument of claim 1, wherein the spring urges thesecond collar toward the body.